1. Field of the Invention
The present invention relates generally to media support structures, and more particularly to a media support structures which improve edge-to-edge printing.
2. Description of the Related Art
Digital photo printing has increased in popularity in recent years due to the increased popularity of digital cameras. Generally, digital cameras convert an optical image to a digital image through a charge-coupled device (CCD) image sensor or the like. The digital image may then be saved to an image memory for further data processing. In recent years digital camera features have improved significantly. For example, digital camera resolutions and memory storage capabilities have increased while prices for such features have steadily decreased, leading to increased digital camera sales. As a result of increased use of digital cameras, edge-to-edge photo printing has increased. Users desire developed pictures having the look, feel and size of photos developed by professional developers.
Manufacturers have developed various photo printers which print the digital images to media comparable to professionally developed photos. Current manufacturers have primarily utilized inkjet technology in order to obtain high quality photo prints. In conventional inkjet printers, there may be a carriage having one or more ink cartridges removably mounted therein. Each cartridge may utilize a printhead for directing ink to a media sheet passing adjacent thereto. The carriage unit is adapted to sweep the ink cartridge in a path of travel adjacent to the media, which is typically moved in a transverse or orthogonal direction to the carriage unit. As the printhead sweeps or scans adjacent the media, ink droplets are ejected onto the medium sheet which is typically supported from below by a platen.
In conventional inkjet printing, manufacturers have strived to avoid ink smearing on the underside of a media sheet. Smearing may occur when ink is misdirected onto printer components adjacent the feedpath and the media touches such component. One way of avoiding ink on printer components is to form margins. Accordingly, conventional printers inhibit ejection of ink onto the leading, trailing, and side edges of the medium sheet. This creates sheet margins, and in turn, protects the upper surface of the supporting platen from receiving ink droplets being ejected by the printhead. However, the advent of photo printing has led to a desire to print borderless images, which appear similar to professionally developed photographs.
Manufacturers have encountered difficulty in providing a detailed photo image up to the media edge, also known as edge-to-edge printing. As media leading edges and trailing edges pass through a print zone, the media tends to sag or bend, resulting in changing of the distance between the printhead and media making edge printing difficult. One manufacturer has employed the use of a trough filled with an absorbing foam for the sprayed ink. Projecting through the foam and extending from the bottom of the trough and centered between the two walls of the through is single row of a plurality of narrow column-like structures, each having a relatively broad rounded-over top. The column tops extend above the top of the foam and support the underside of the media during its travel through the print zone. One drawback with this approach is the width of the supports. The relatively large area of the support becomes an area where the sprayed ink can accumulate and possibly smudge the undersurface of the media. Also a large number of support columns are used along the length of the through increasing the chances of ink accumulation and smudging.
To ensure that there are no blank areas along the media edges and to compensate for positional errors, the printhead must also fire ink from nozzles which are slightly beyond the edge of the media. Thus, the printed area will include the edges of the media and eliminate blank areas therealong. However, since the media must be oversprayed to ensure printed ink along the edges, ink ejected from the nozzles spreads to areas where media does not exist and may adhere to the printer components generally adjacent the print zone, such as the platen or ribs. When a subsequent medium passes through this area, ink may be smudged on a surface of the media facing the platen or ribs.
Another difficulty which printer manufacturers have struggled with is maintaining a constant distance between the printhead and the media. This causes a change in distance between the printhead and the media being printed on and further results in decreased print quality especially along media edges. It is preferable that a gap between the nozzles of the printhead and the media must always be maintained constant since any change in distance may adversely affect photo print quality. However, due to the water content of ink, the media is subject to a phenomenon known as “cockle” consisting of swelling and expansion of the media during printing. When cockle occurs, the media forms bubbles and wrinkles and, as a result, the distance between the paper and printhead decreases in some areas. As a result, the distance between the printhead and media changes. The cockling of the media may also result in “vertical banding” because the bubble in the media may cause the ink dots to fall in positions offset from their correct position, e.g. all displaced toward the same side, leaving visible marks on the plot in the form of parallel lines. These issues also increase the difficulty of edge-to-edge printing.
Given the foregoing, it will be appreciated that an apparatus is needed which supports media moving through a print zone at a substantially constant distance from the printhead and also inhibits ink smearing on subsequent media.